US2572693A - Rotational viscometer - Google Patents

Description

Oct. 23, 1951 Filed April 19, 1949 A. R. BOYLE ROTATIONAL VISCOMETER 6 Sheets-Sheet 1 FIG].

Inventor Jim/1m [4mm 30m Attorneys A. R. BOYLE ROTATIONAL VISCOMETER Oct. 23, 1951 Filed April 19, 1949 6 Sheets-Sheet 2 Inventor Aim/5,410 16mm B0 71;

Attorney Oct. 23, 1951 A. R. BOYLE ROTATIONAL VISCOMETER 6 Sheet s-Sheet a FiIed April 19, 1949 I nventor mmm AA mm; 50 Y1! Aidm 9W a 44% Oct. 23, 1951 A. R. BOYLE ROTATIONAL VISCOMETER' 6 Sheets-Sheet 4 Filed April 19., 1949 Inuenlor Attorney Oct. 23, 1951 A. R. BOYLE 9 ROTATIONAL VISCOMETER Filed April 19, 1949 6 Sheets-Sheet 5 Attor neys Oct. 23, 1951 A. R. BOYLE 2,572,693

ROTATIONAL VISCOMETER Filed April 19, 1949 6 Sheets-Sheet 6 FIGS.

DIRECT PHASE C'Q v A as 359 PHASE T/REVS. P512 55c.

77/?5 vs.- PER SEC.

5 Inventor jaw/mm 1?;17/70N0 8on4" N A Horn e ys Patented Oct. 23, 1 951 ROTATIONAL VISCOMETER Archibald Raymond Boyle, Glasgow, Scotland,-

assignor to Dobbie Mo Scotland Innes Limited, Glasgow,

Application April 19, 1949, Serial No. 88,327 In Great Britain April 21, 1948 This invention relates to rotational viscometers for measuring the viscosity of liquids, semi-liquids, or like fluent materials (hereinafter and in the claims referred to simply as liquids), in which a rotational body is rotated by an electric motor, the current in said electric motor being measured and being a measure of the viscosity of the liquid in which the rotational body is driven.

In accordance with the present invention, we provide a rotational viscometer comprising a body adapted to be rotated in a liquid under test, a two-phase electric motor adapted to be fed from a single-phase supply and to rotate said body, a reactance connected in one phase of said motor of a value which causes resonance to occur in that phase at approximately synchronous motor speed, and means for measuring the current in the other phase (hereinafter called the direct phase).

The rotational body may be placed in the liquid under test, or the liquid under test may be fed through a space in which the rotational body moves.

In one example the stator and rotor of the electric motor themselves define a passage through which the liquid under test passes.

Some embodiments of the invention will now be described simply by way of example with reference to the accompanying drawings in which- Fig. 1 is a circuit diagram showing the electrical parts of a viscometer in accordance with the invention.

Fig. 2 is a cross sectional plan view on the line II-II of Fig. 3 illustrating a construction in which the electric motor stator and rotor themselves define a passage for the liquid under test.

Fig. 3 is a sectional elevation on the line IIIIII of Fig. 2.

Fig. 4 is an outside perspective elevation partly 9 Claims. (Cl. 73--59) broken away for clearness showing some details oi the arrangement shown in Figs. 2 and 3.

Fig. 5 is a perspective view of a complete viscometer.

Fig. 6 is a detail axial section through the stator of the viscometer shown in Fig. 5.

Fig. 7 is a perspective view of a further complete viscometer.

Fig. 8 is a detail axial sectional view showing the rotor of the viscometer of Fig. '7.

Figs. 9 and 10 are curves illustrating the functioning of the circuit shown in Fig. 1.

Fig. 11 is a circuit diagram similar to Fig. 1, but showing a modification in which the viscom- I eter is combined with varyingthe speed of rotation thereof over a given range inorder to obtain a continuous flow dia ram..

In Fig. 1' the electric motor comprises a rotor II, with stator windings I2 and [3 arranged in two phases at electrical apart, the winding I2- having a condenser I4 in series therewith (this constituting the-condenser phase) and winding I3 having acurrent measuring instrument I5 in series therewith (constituting the direct phase) of a body through a liquid, by definition the viscosity of theliquid is directly proportional to the shear force of the body divided by the rate of shear. The shear force multiplied by the torque arm is equivalent to the actual torque value, while the rate of shear may be stated in terms of revo..

lutions per second of the body (revs. per sec.).

Now in any electricmotor the current input is.

a function of the ratio torque divided by speed of rotation, or that ratio isequivalent to the viscosity multiplied by a constant.

From this it follows that the viscosity of the.

liquid is a function or. measure of the input current. Under the present invention the current in the direct phase l3, I5 is measured and this provides certainimportant advantages as here-;

inafter explained. The synchronous speed of the motor is deter-: mined by the supply frequency and the number of poles on the motor.v Knowing this in advance, the capacity of the condenser I4 is selected to. give the circuit a natural periodicity correspond. ing to such synchronous speed, whereby reso,- nance occurs in the circuit at or about synchroa or maximum resonance with minimum current in. the direct phase and. maximum current in the:

condenser phase. The resonance curve is dampedsomewhat by the resistances of rotor and stator. If the total input current of the two phases is measured, this would be a combination of the; curves MTU and ABS which would give a more-- or less level line. .The current measured in the" direct phase is approximately a reflection but in the opposite sense of thecurrent in the COIk;

denser phase within the working range, but the means for automatically:

curve of current} The two curves are not completely symmetrical and thus the resultant change in the total current taken by the two phases together involves a smaller change than that in the direct phase alone. By measuring the current in the direct phase only a considerable magnification is obtained at or adjacent to the resonant part of the curve, the working part corresponding to AB which corresponds approximately to a straight line. Thus a small change in viscosity can give a relativelylarge change in the measured current.

Fig. 10 shows, for the same co-ordinate axes, at ABS, ABQ and ABE, typical curves for the direct phase corresponding to applied voltages varying by approximately plus or minus 20% ABP, corresponding to a voltage approximately 20% below ABS and ABQ corresponding to a voltage approximately 20% above ABS. It is possible by applying normal design principles to arrange that a series or such curves coincide over the Working range so that the current in the direct phase is independent of reasonable variations in the applied voltage; this may be effected, for example, by selection or the number of turns on the stator, and by design oi the resistance of the rotor and stator parts. 7,

1n contraoistmction, with variations in the applied voitage, the current in the condenser phase Will vary over the whole range, 1. e., the curve M'lU would be translated upwards or downwards. 'Ihusthe. current in the condenser phase within the working range wouldnot be independent or the applied voltage. V

With the circuit shown in Fig. 1, it is possible by normal design methods to vary parts of the circuit such as the gap in the iron circuit, the resistance of the rotor strips or bars, and the number of poles in the coils, to obtain advantageous results as follows:

(1 The working partAB of the direct phase is a substantially straight line.

(2). The gradient of the part AB can be predetermined and can. be. made substantially steep so as to obtain a. relatively large variation in current for a, relatively small variation in viscosity.

(3) The height. A canbe kept small. Electric a-lor mechanical backing. on. methods. are used on the indicating meter [5 to make use of the full scale. thereon, that is, to. minimise the amount of non-useful movement of the indicator up to'th'e point where the minimumcurrent, is indicated, and for efiiciency, such. backing off should be kept to a small percentage of the full scale indication. Referring to Fig. 9, theamount of backing off required for measuring in the direct phase corresponds to 0A, this corresponding to the initial movement of the indicator up to the point of minimum current. On the condenser phase the point of minimum. current (within the working range) is at T, showing a backing goff corresponding to the height NT which is much greater.

It will be clear therefore that by measurement of th'e current consumption in the direct phase important advantages are obtained over either measurement of the total input current of both phases, or measurement in the condenser phase only, because firstly substantial magnification is obtained; secondly the current is independent of variation in applied voltage; and thirdly a :rela' tiv'elysmall amount of backing off is required.

In use, the motor is continuously driven, and if the viscosity increases the motor speed dro s.

down until the viscosity drag is balanccdby the resistivity, for example glass or. alloy metal, may

torque of the motor, and then a reading of the current provides a measure of the viscosity. Similarly when the viscosity falls the motor increases speed until balance is again obtained, when a fresh reading is given.

In Figs. 2, 3 and 4, the viscometer is formed within a casing I! and comprises stator l8 and rotor IQ of a two-phase motor, the rotor l9 being of squirrel cage type connected as in Fig. l. The liquid under test flows through the passages 23 and 2| in the direction shown by the arrows and a proportion thereof is by-passed through passages 22, 23, provided with valves 22a, 23a so as to flow continuously through the space 24 between the rotor and stator.

Figs. 2 and 3 are somewhat diagrammatic and Fig. 4 shows some external details of the practical embodiment, the valve 22a corresponding to that shown diagrammatically in Figs. 2 and 3 and being mounted in watertight manner in the casing I1 and provided with an externally operated handgrip.

The rotor spindle is shown at 25 and is mounted in watertight manner in the casing being secured in position in a bearing 26 at each end, said bearings each being enclosed by a cover 21.

The bearings for the rotor should have the minimum of friction and of viscous drag and may,

as shown, comprise cones or points on the rotor mounted in corresponding jewelled sockets screw set in the casing, any leakage through the bearing thus being avoided; alternatively a ball and plate or ball and. ball construction can be utilised.

The electric leads to the stator coils enter through a screw junction box having a gland 28, and cables may be included for temperature com-'- pensation purposes, for example for measuring the temperature of the liquid, and/or for ther mostati'cally controlling theteinperature of the liquid in the space between the rotor and stator.

Wherever required cement may be provided to ensure a leak-proof seal.

A viscometer as shown in Figs. 1 to 4 may be used for various purposes, for example, for measuring the variation in viscosity of a liquid flowing.

through ahigh pressure pipeline or other vessel,

variation in that characteristic. causing variation in the externally measuredcurrent of the electric motor direct phase; and this in turn may bring into operation a consequential control.

In Fig. 5, the viscometer comprises an electric motor 29 of similar type to that already .de-' scribed and which is vertically adjustable on a guide 30, the rotor having a depending spindle :3!

having a rotational element32 which canthus be immersed in the liquid under test. The varia tion of current in the direct phase is measured by a remote current measuring device, and this arrangement may be utilised for example, for in;- dicating when -'a chemicalyorphysical characteristic in a li'quidhas reached. agiven stage.

It is usually advisable to :protect the stator and rotor windings from contact with. theliqui'd, and this may be done for example by first thoroughly impregnating the windings and. then covering the complete windings and;lam-inations witlia nonfconducting, -non-n 1agneticv cement, for example synthetic resin cement. The interior of the statorand the exteriorof the rotor are then ground to the correct. shape. gives smooth working surfaces- In a modification a covering of hon -magnetic, corrosion resisting material. and ,high electrical This arrangement.

be fitted around the rotor and possibly another around the stator, and it is advisable to back the coverings with a cement.

As shown in Fig. 6, the stator 33 of the motor is provided with a covering 34, and has windings 35 bedded in heat proof cement 36.

Only one half of the stator is shown in Fig. 6, the other half being of identical construction.

In Fig. '7, the motor 3! is vertically adjustable on a guide 38 and the current in the direct phase is measured remotely through a conductor 39.

Operation of handle 40 in the downward direction causes the rotor extension 4| to be moved downwardly along with the detachable outer sleeve 42 in order to immerse them in the liquid 43 under test, which is shown by way of example in a container 44.

In this construction the gap between rotor 4| and sleeve 42 can be varied by interchanging sleeves of different internal diameters, thus changing the range of operation of the viscometer depending on whether liquids of high or low viscosity are to be measured.

The rotational bod may be of any convenient shape instead of cylindrical as shown, for example, it may be of rotary blade form, or may comprise a plate sliding rotationally on a fixed plate, with the liquid as a film between them.

The rotor is usually of squirrel cage construction, although a wound rotor may be utilised.

The range of the viscometer may be varied by altering the mechanical or electrical characteristics thereof, for example the gap width at the rotational body, the length of rotor and stator,

or the diameter of rotor; moreover the number of stator poles can be altered, the greater the number of poles the higher the range. Further, a portion of the indicating scale for indicating the current consumption may be selected and electrically amplified, or the frequency of the supply may be changed.

Alternatively, variable gearing may be provided between the motor shaft and the rotational body. As the viscosity reading is then approximately proportional to the square of the gear ratio it is found most convenient to make the gear ratios 1:1, :1, 100:1, and 1000:1. This means that the scale readings are approximately multiplied by 100 for each gear change.

It is of course possible to place the milliammeter or other viscosity indicator in any desired position within reasonable limits, and to have any number of milliammeters in various positions in this circuit. The gear change may be operated by a relay, if desired, to change the range from a remote position.

Automatic control of apparatus may be obtained by using the change of measured current to operate appropriate changes in the liquid flowing into the viscometer, by use of servo mechanisms or the like.

In industrial plants the viscosity reading scale may be colour-coded, and by way of example, the needle is normally maintained over a certain coloured area of the scale as long as the plant is running correctly. Automatic alarms can be made to operate if the milliammeter position alters beyond this range.

Recording galvanometers may be attached to give a clear record of changes in viscosity, either as a check on the constancy of a product, or to measure and control expected changes during a chemical reaction.

The apparatus may be used as a static instrument in a laboratory if desired, but its greatest advantages appear when it is used on an industrial plant, for example in a vat or pipe-line, or in side tubes attached to them. In order to make certain of rapid indication of changes in viscosity a slight rifiing or other similar grooving or ridging, may be machined onto the surface of the rotational body in order to ensure positive flow of the liquid through the viscometer.

When, for example, in an industrial plant, the temperature of a liquid in a pipe-line varies, temperature eifects can be compensated by using thermometers, for example, platinum resistance, or thermocouples, in the viscometer, or in a position in the liquid nearby, and indicating on dials preferably adjacent to the viscosity dial.

To indicate a viscosity result corrected for a temperature other than the temperature of test, the electrical outputs of thermometer and viscom-- eter may be electrically mixed.

When the layer of liquid in the viscometer is thin, that is, of small mass, a thermostatically controlled arrangement around the cylinder will correct for small changes in temperature even when the flow speed is fairly high.

When very high accuracy of indication is desired a circuit may be used in which a small portion of the milliammeter scale is taken and ex panded. This may be brought about by a suitable increase in sensitivity of the milliammeter and the application of a suitable backing oif voltage fed directly from the supply or battery to bring the expanded range onto the scale of the milliammeter.

For a true liquid this ratio of shear divided by rate of shear is constant for various speeds of rotation, that is with variation of the voltage applied to the motor.

This true liquid is known as a Newtonian liquid. However, for other types of liquids known as non-Newtonian liquids, for example emulsions, or suspensoids, or colloids, the apparent viscosity thereof as measured in the viscometer changes with change in the rate of shear owing to the effect of the rotation of the viscometer on the particles although the physical characteristics of the liquid outside the viscometer are unchanged.

I have found that the viscosities of such non- Newtonian liquids may be compared with a standard viscosity or with their own viscosity at a given rate of shear by comparing the fiow diagram thereof, that is the diagram showing the;

variation of the apparent viscosity with varia tion of rate of shear, that is of speed of the viscometer.

Thus, in further accordance with the invention, there is provided a rotational viscometer as aforesaid, in combination with means for automatically varying the speed of rotation thereof over a given range, and means for making a continuous record of variation of the measured (i. e., the apparent) viscosity against variation of the speed. This enables a continuous flow diagram to be obtained and hence one can compare the viscosity of the liquid under test with any standard liquid at any speed, whether a Newtonian or non-Newtonian liquid.

This arrangement may conveniently be effected by providing a synchronous motor adapted to vary a potentiometer governing the supply voltage of the viscometer. Thus the supply voltage is varied between maximum and minimum limits automatically; the variation may be uniform or in accordance with any predetermined law.

fiefer ring to Fig. 11, the parts shown eerie: spend to Fig. l, the same numerals indicating similar parts, but a potentiometer 45-is incorporated in the secondary circuit of the transformer I], the arm 46 of the potentiometer being continuously rotated by a synchronous motor 41 through a reduction gear box. In this Way a continuous record of variation of the measured viscosity against variation of speed of the viscometer is obtained as aforesaid.

I claim:

1. A rotational viscometer comprising body adapted to be rotated in a liquid under test, a two-phase electric motor adapted to be fed from a single-phase supply and to rotate said body, a reactance connected in one phase of said motor of a value which causes resonance to occur in that phase at approximately synchronous motor speed, and means for measuring the current in the other phase. g

2. A viscometer as claimed in claim 1, in which the electric motor comprises a stator and rotor which define between them a gap for the liquid under test, the rotor constituting said rotatable body of the viscometer.

3. A viscometer as claimed in claim 2, comprising a first conduit for the liquid which causes a portion thereof to by-pass the gap between the stator and rotor, and a second conduit which causes a portion of the liquid under test to be passed through said gap.

4. A viscometer as claimed in claim 1, in which the motor rotor constitutes the rotatable body and the stator and/or the rotor is or are totally enclosed in a protective external sheath.

5. A viscometer as claimed in claim 1 in which the motor rotor constitutes the rotatable body, and the rotor spindle is extended so as to project substantially clear of the stator so that the extremity thereof may easily be inserted in a container for the liquid under test.

6. A viscometer as claimed in claim 1, in

which the'moto'r rotor constitutes the rotatable body and the rotor or one end thereof is-movable axially of the stator in order to cause it to be projected axially intoor to be withdrawn axially from the liquid under test.

'7. A viscometer as-claimed in claim 1, in combination with means for automatically varying the speed of rotation thereof over a given range, and means for making a continuous record of variation of the measured viscosity of the liquid under test, against said variation of the speed.

8. A rotational viscometer comprising a twophase electric motor adapted to be fed from a single phase supply, a rotor for said motor, a rotor spindle extended so as to project substantially clear of the motor stator so that the extremity thereof may easily be inserted in a container for the liquid under test, sleeve means at least partly surrounding that part or the rotor extension adapted to-enter the liquid under test, said sleeve means providing a clearance with such extension, a reactance connected in one phase of said motor of a value which causes resonance to occur in that phase at approximately synchronous moto speed, and means for measuring the current in the other phase.

9. A viscometer as claimed in claim 8, in which said sleeve means is removable so as to be interchangeable with other sleeve means in order to vary said clearance with the rotor extension and thus vary the sensitivity of the viscometer. ARCHIBALD RAYMOND BOYLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,449,458 Sutermeister Mar. 2'7, 1923 1,942,920 Fawkes Jan. 9, 1934 2,354,923 McNamee Aug. 1, 1944

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